Assorted improvements to Command* classes

Improved robustness, functionality, and documentation of Command* classes

Also, when a valid command packet is processed, a command is now always added to the queue with HEROES command key 0x10ff, SAS command key 0xffff, and a uint16_t payload containing the sequence number.  This command comes before any parsed commands, and is intended to facilitate the creation of the 0x01 acknowledgement telemetry packets.